A preliminary assessment of water quality conditions in Kempenfelt Bay and adjacent Lake Simcoe indicates that localized enrichment in the vicinity of Barrie has occurred. This fact is supported by higher phosphorus concentrations in the west end of the bay and production of the alga Cladophora in the same vicinity. While phytoplankton production (as reflected by chlorophyll analyses) is quite low throughout the bay, comparative evaluations of dissolved oxygen levels at various depths and analyses of bottom fauna communities suggest an increase in the quantity of phytoplankton and possibly other organic solids settling to the bottom in recent years. This has caused oxygen depletion in the deeper waters and a corresponding shift in benthic communities from a dominance of midge larvae to more pollution-tolerant sludgeworms. The implications of these changes on the fishery resources of the lake is a point of major concern. Elimination of existing artificial nutrient sources and provision of adequate nutrient containment associated with all future development will be necessary to minimize further effects resulting from aquatic enrichment. This study has suggested the need for a more comprehensive evaluation of the impact of all existing municipal and industrial development, cottage development and agricultural practices on the water quality of Lake Simcoe. This has been scheduled for the summer of 1971. Clean water in Lake Simcoe is of paramount importance when we consider its size, it diverse recreational potential, including excellent fishing, and its proximity to the most densely-populated area of Ontario.